Field of the Invention and Description of the Related Art
This invention relates to an endoscope apparatus which is equipped with a signal processing means enabling monochrome images with respect to specific wavelength components to be diplayed as well as color images by visible light, so that the diagnostic functions thereof may be substantially improved.
Recently, television cameras using a solid image pickup elements such as CDD as the image pickup means are being widely used. Such image pickup means have also come to be used in endoscopes.
Conventionally, a visible light image (ca. 400 to 700 nm) is picked up by means of said CDD or the like and is transformed into a video signal, to be color-displayed on an observation monitor. As a result, what can be obtained are the same images that one can see with the naked eyes while using a fiber scope. As to the diagnostic functions of an endoscope using such image pickup means, they are not very much different from those of a fiber scope.
In view of this, a picture processing or a picture analysis has been performed on the image signals of the endoscope, from which the following have become apparent:
(a) The inner celom walls have colors of various shades of red. However, it is appreciated, by depicting them with the red component alone, that they contain few high-frequency components (fine variations on the subject present no great contrast) and give a flat or hazy impression, thereby detriorating the contrast for the entire visible wavelength region.
(b) On the other hand, the red component excels in mucosal permeability and is more useful in depicting sub-mucosal blood vessels than the green and blue components. In other words, when observing sub-mucosal vessels, the green and blue components deteriorate the contrast in the images.
(c) The green component, to which the human eyes are highly sensitive, is the main contrast factor in an endoscope. Further, it conveys more information than the blue component (the inner celom walls present intrinsically little blueness, and solid image pickup elements have generally poor sensitivity to blue), so that they can provide images with a satisfactory S/N. Since the blue component has a short wavelength, it is reflected at positions which are quite near to the surfaces of the inner celom walls. Accordingly, it is useful in depicting fine surface irregularities.
However, it would render the image quite uncomfortable to watch to display exclusively the red component as red, the green component as green, and the blue component as blue. An appropriate light intensity adjustment could not then be effected, either,